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Investments (Tables) | 12 Months Ended
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Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract] |
Summary of investments | The following is a summary of available-for-sale securities as of December 31, 2017 and 2016:
|  |  | As of December 31, 2017
| Contractual Maturity (in years) | Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Fair Market Value
Mutual funds | --- |  | $ | 68,776,165 |  |  | $ | 42,097 |  |  | $ | (252,373 | ) |  | $ | 68,565,889 |
US corporate debt securities | Less than 2 |  | 35,210,121 |  |  | 3,032 |  |  | (140,198 | ) |  | 35,072,955 |
Investment in affiliated entity (PLS) | --- |  | — |  |  | 2,325,079 |  |  | — |  |  | 2,325,079 |
Total investments |  |  | $ | 103,986,286 |  |  | $ | 2,370,208 |  |  | $ | (392,571 | ) |  | $ | 105,963,923 |
|  |  | As of December 31, 2016
| Contractual Maturity (in years) | Cost |  | Gross Unrealized Gains |  | Gross Unrealized Losses |  | Fair Market Value
Mutual funds | --- |  | $ | 60,883,065 |  |  | $ | 94,374 |  |  | $ | (387,693 | ) |  | $ | 60,589,746 |
US corporate debt securities | Less than 2 |  | 25,098,122 |  |  | 6,853 |  |  | (65,309 | ) |  | 25,039,666 |
Investment in affiliated entity (PLS) | --- |  | — |  |  | 3,777,510 |  |  | — |  |  | 3,777,510 |
Total investments |  |  | $ | 85,981,187 |  |  | $ | 3,878,737 |  |  | $ | (453,002 | ) |  | $ | 89,406,922 |

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- Definition Tabular disclosure of the reconciliation of available-for-sale securities from cost basis to fair value. + References No definition available. + Details
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